In order to reduce air pollution, there is a modern trend toward electrically powered automobiles. These electrically powered automobiles have rechargeable batteries therein. The power of the batteries is used to propel the automobile and to provide for other power needs thereof. The design of such a vehicle is a careful balance between payload, performance, range between charging, acceleration, and speed. No matter what the combination of these criteria, there is need to recharge the batteries periodically so that the automobile may be taken on another excursion. With fairly large battery capacity, there is need to recharge a substantial amount of power. Since the time when an automobile is unavailable should be minimized, high charging rates are desirable. If an ordinary plug is to be used, the plug must be suited for high power, which brings about a risk of harm to the operator and/or other people in the vicinity from contact with parts of the electrical supply system.
It is, thus, desirable to make a coupling between the charging station and the automobile which does not require the direct transfer of electricity. A magnetic coupling is desirable. In accordance with this invention, an inductive charge coupler can be manually handled and inserted in an appropriate inductive charge receptacle slot in the automobile. The inductive charge coupler is a transformer primary and contains an appropriate magnetic conductor. The inductive charge receptacle slot contains the secondary winding(s) together with the rest of the magnetic core. The transformer secondary in the automobile is connected through appropriate electrical equipment to the battery for the charging thereof.
The frequency is preferably much higher than the ordinary power line frequency for advantageous coupling, and high charge rates are above 10 kilowatts. The result is that there are losses in the coupling system which result in heat. The amount of heat dissipated from the transformer coils, magnetic coils and other electronics contained within the inductively coupled connector transformer container can exceed 50 watts. In order to minimize the temperature rise of the equipment, the losses should be minimized. The primary inductive charge coupler is preferably cooled. It is desirable to keep the temperature level of the inductive charge coupler within tolerable, comfortable limits. In addition, it is desirable to cool the entire transformer so that its internal temperatures do not exceed the operating range of the materials used in the connector housing.
Cooling could be achieved in the automobile, but it is desirable to limit the total automobile weight as much as possible. It is, thus, desirable to improve the cooling methods for the inductively coupled charging connection. It is also useful to employ offboard cooling sources to cool the transformer primary coil and magnetic core efficiently in the inductive charge coupler. This offboard cooling reduces the entire primary transformer structure and reduces the surface temperature of the removable inductive charge coupler.
Losses, and consequently heating, can be reduced by design of the coils and their location. The AC resistance losses (the eddy current losses) are reduced by reducing the number of consecutive layers in the axial direction of the magnetic field. By separating the coil layers, in both the primary and secondary, a greater surface area is achieved so that there is increased surface area across which cooling air may flow.